1. Field of the Invention
This invention relates to a control device for controlling a permanent magnet motor serving as both an engine starter and a generator in motor vehicles.
2. Description of the Related Art
A starter (self-starting motor) is usually coupled via a clutch with an output shaft of an engine in motor vehicles such as automobiles. The starter is electrically connected via a relay switch to a battery. A dynamoelectric generator is connected via pulleys and belts to the output shaft of the engine. The generator is further connected to the battery. When an ignition key is turned so as to assume a starter position so that a starter relay is operated, a relay switch is turned on so that power is supplied from the battery to the starter. As a result, the starter is rotated so that the output shaft of the engine is rotated, whereupon the engine starts. Thereafter, a clutch is released and the starter relay is returned so that the relay switch is turned off. Upon starting of the engine, the generator is driven for power generation, so that the battery is recharged.
In the above-described construction, both engine starter and generator for re-charging the battery are required. The requirement results in an increase in a mounting space of the automobile. Furthermore, a large current flows into the starter in starting the engine in order that a large torque may be developed. Accordingly, the starter relay is required to be large sufficiently to withstand the large current flowing into the starter. Additionally, the clutch is provided to prevent the starter from reverse drive by the engine. The clutch further increases the mounting space of the automobile.
Therefore, an object of the present invention is to provide a control device for controlling a permanent magnet motor serving as both an engine starter and a generator in a motor vehicle, which control device can reduce the mounting space of the motor vehicle and can eliminate a large starter relay.
The present invention provides a control device for controlling a permanent magnet motor serving as both a starter for an engine and a generator in a motor vehicle, the engine including an output shaft to which the permanent magnet motor is connected, the motor vehicle including a battery. The control device comprises a drive circuit converting a direct current to an alternating current to supply the alternating current to the permanent magnet motor, the drive circuit having at least one arm including two series connected first switching elements having flywheel diodes respectively, the drive circuit having an input terminal connected to a capacitor and an output terminal connected to the permanent magnet motor, a chopper circuit including a plurality of series connected second switching elements having diodes connected in parallel with the second switching elements respectively, the chopper circuit being disposed at the battery side and connected in parallel with the capacitor, a reactor connected between a neutral point of the chopper circuit and the battery, and control means for controlling the switching elements of the drive circuit and chopper circuit so that the switching elements are turned on and off.
In the above-described arrangement, the permanent magnet motor is connected to the output shaft of the engine so as to serve as the starter for the engine. The permanent magnet motor further serves as the generator recharging the battery after starting of the engine. Thus, the single permanent magnet motor is used as the starter and the generator. Consequently, the mounting space of the motor vehicle can be reduced as compared with the conventional construction in which both starter and generator are individually provided. Furthermore, since no clutch is required between the engine output shaft and the permanent magnet motor, the mounting space can further be reduced. Additionally, the permanent magnet motor is driven by the drive circuit controlled by the control means when operated as the starter. Accordingly, no relay switch as a starter relay is required between the battery and the permanent magnet motor. Consequently, a large starter relay is not required.
In a preferred form, when the permanent magnet motor is operated as the starter, the control means renders the chopper circuit non-operative or causes the chopper circuit to operate as a step-up chopper so that the control means controls the drive circuit to drive the permanent magnet motor. When the permanent magnet motor is operated as the generator, the control means renders the drive circuit non-operative and causes the chopper circuit to operate as a step-down chopper so that the battery is recharged, in case voltage generated by the permanent magnet motor is higher than voltage of the battery. In case the voltage generated by the permanent magnet motor is lower than the voltage of the battery, the control means renders the chopper circuit non-operative and turns on and off the negative switching element of the drive circuit so that the drive circuit is caused to operate as a step-up chopper so that the battery is recharged.
In another preferred form, the control device further comprises another chopper circuit connected in parallel with the chopper circuit and including two series connected switching elements having diodes connected in parallel to the switching elements respectively, and another reactor connected between a neutral point of said another chopper circuit and the battery. In further another preferred form, the control means turns on and off the negative switching elements of the two chopper circuits with a timing phase difference by 180 electrical degrees in a case of voltage step-up and turns on and off the positive switching elements of the two chopper circuits with a timing phase difference by 180 electrical degrees in a case of voltage step-down. Additionally, each of the reactors preferably includes a single core and two coils wound on the core.